Twenty-six countries have continued searching two vast arcs of land and sea for the missing Malaysia Airlines jet, with no sign of a breakthrough in the investigation 11 days after flight MH370 vanished.

The search area now covers 2.24m square nautical miles – an area larger than Australia and stretching from central Asia down to the southern Indian Ocean.

The Boeing 777 vanished early on 8 March en route from Kuala Lumpur to Beijing with 227 passengers and 12 crew on board. Malaysian officials have said they believe the plane was diverted deliberately but are not ruling out any possible reasons for the change of course.

Police in the Maldives said they were investigating reports that people on one of its outer islands had seen a low-flying plane early on 8 March but gave no further details. Media reports have suggested that residents saw a low-flying white plane with red or blue markings but there have been previous potential sightings that do not appear to have been borne out, adding to the anguish of waiting families.

“Personally I hope it has been hijacked and she is still alive,” said Wang Yongzhi, from Beijing, whose wife was on flight MH370. “But from a practical, scientific point of view I know it has been quite a long time. Probably bad luck outweighs the good.”

On Tuesday Malaysian officials urged countries on the plane’s potential path to reanalyse their military radar data in the hope of narrowing down the area – which comprises two great arcs sweeping north towards Kazakhstan and deep into the southern Indian Ocean far off the coast of Australia.

A coalition of 26 countries is looking for the aeroplane, which vanished on 8 March with 239 people aboard en route from Kuala Lumpur to Beijing. China said it had deployed 21 of its satellites.

Several countries including Laos and Kazakhstan have said there is no evidence MH370 entered their airspace after diverting from its route to Beijing.

“This is an enormous search area. And it is something that Malaysia cannot possibly search on its own,” said the Malaysian transport minister, Hishammuddin Hussein. “All efforts are being used now to reduce the [search] area – looking at satellite data; seeking assistance from other friends who have satellite capability; asking if they have looked [at radar data] to relook at them; finally, the use of assets whether in air or at sea.”

Thailand was criticised for taking 10 days to state that its military radar information appeared to back up Malaysia’s own data about the plane’s apparent passage over the Malacca Strait. The Thai authorities said they did not release the details earlier because they had not received a specific request.

Ian Storey, a senior fellow at Singapore’s Institute of Southeast Asian Studies, told Reuters: “Information and intelligence exchange is very sensitive in this part of the world where there is a lot of distrust and sovereign issues.

“Countries are unwilling to share sensitive intelligence because it reveals their military capabilities – or lack of capabilities.”

Hishammuddin said China and Kazakhstan were taking the lead in the search of the northern arc, while Indonesia and Australia were taking charge in the south.

Earlier the Chinese ambassador to Malaysia said the country had begun searching its own territory for any sign of the plane. Huang Huikang also said extensive checks on all Chinese passengers on board MH370 found no evidence they were involved in the diversion of the plane.

A multinational team of investigators has established that the plane’s last contact with satellites was at 8.11am but so far they have not fixed its location at that time any more specifically than along the sweeping search arcs. More than 150 Chinese nationals were among the 239 people on the Beijing-bound flight when it disappeared. Investigators say they are looking into the background of all crew, ground staff and passengers.

State news agency Xinhua reported that the country’s premier, Li Keqiang, rang the Malaysian prime minister, Najib Razak, on Monday asking him to provide Beijing with more detailed and timely information.

While China has urged Malaysia to be more transparent, its foreign ministry spokesman, Hong Lei, declined to give any details of its own search – such as when it began to search its own territory, which agencies were involved and what regions were covered.

With so many days having passed since the plane disappeared, some now wonder if the puzzle may ever be solved: “It’s a mystery and it may remain a mystery,” says Elizabeth Quintalla, chief air power researcher at the Royal United Services Institute in London.

The lack of progress in the investigation has bred numerous theories about the case, from prosaic discussions of possible mechanical failures to highly outlandish conspiracy theories. Few seem capable of explaining the disappearance entirely but with so few facts available it is hard to disprove any of them.

“There are all these polarising theories with so little definitive information that is verified,” Paul Yap, an aviation lecturer at Temasek Polytechnic in Singapore, told Agence France-Presse.

“Everything that is not denied so far is being considered to be true, making a lot of theories quite plausible and that makes it even more difficult.”

One theory that has emerged is that some kind of emergency prompted the pilots to divert to attempt a landing on a Malaysian runway, turning the flight westwards.

The transponder – an identifying device that replies to radar signals from the ground – appears to have switched off two minutes after the last verbal communication with air traffic control. The Malaysia Airlines chief executive, Ahmad Jauhari Yahya, said a malfunction could not be ruled out. While an onboard plane-to-ground monitoring system known as Acars had stopped sending data back to base, the plane’s satellite transmitter had continued to communicate its presence to satellites until 8.11am.

“There [was] some functionality in the system, except the reporting system was disabled,” he said.